1. Field of the Invention
The present invention relates to a medium conveyance apparatus and an image forming apparatus, and more particularly to medium secure supporting technology and medium conveyance technology for suppressing floating of a medium.
2. Description of the Related Art
In an inkjet recording apparatus, guaranteeing the planarity (flatness) of the printing surface (image forming surface) of the recording medium directly below the inkjet head is directly linked to image quality. For instance, if creasing or floating of the recording medium occurs and a prescribed planarity is not guaranteed, then this leads to decline in the image quality, and therefore in an inkjet recording apparatus, various modifications are made in order to guarantee the planarity of the printing surface of the recording medium.
Japanese Patent Application Publication No. 2001-51735 discloses a composition in which a recording medium is vacuum suctioned from the rear side of a printing surface while the recording medium is pressed against a medium holding surface from a printing surface side, by using a roller-shaped pressing member, so as to make tight contact with the medium holding surface, in such a manner that the recording medium is held reliably without floating up from the medium holding surface.
Japanese Patent Application Publication No. 2009-220954 discloses a composition for suppressing floating and creasing of a recording medium by causing a back tension to act on a trailing end of the recording medium. Furthermore, Japanese Patent Application Publication No. 2009-234781 discloses a composition in which a tension is caused to act on the recording medium outwards in a width direction which is perpendicular to the conveyance direction of the recording medium.
Japanese Patent Application Publication No. 11-92008 discloses a composition which holds and conveys a leading end of a sheet by chain grippers provided on an endless chain, in which a roller-shaped vacuum suction wheel is provided on a conveyance path of the sheet, a negative pressure is generated on an outer circumferential surface of the vacuum suction wheel, and a back tension is applied to the sheet by contact (slipping) between the outer circumferential surface of the vacuum suction wheel and the sheet.
Japanese Patent Application Publication No. 2008-280819 discloses a paper conveyance mechanism which conveys paper on a belt, in which a voltage is applied between a paper pressing roller and a supporting roller so as to electrostatically suction and hold the paper until the paper reaches a suctioning device.
However, in the compositions described in Japanese Patent Application Publication No. 2011-51735, Japanese Patent Application Publication No. 2009-220954, Japanese Patent Application Publication No. 2009-234781, Japanese Patent Application Publication No. 11-92008 and Japanese Patent Application Publication No. 2008-230819, it is difficult to guarantee the flatness of the printing surface if the paper is affected by deformation, such as curl. For example, if flapping of the trailing end of the recording medium occurs, or the recording medium has strong curl, then in a composition which presses the recording medium with a roller, as disclosed in Japanese Patent Application Publication No. 2011-51735, Japanese Patent Application Publication No. 2009-220954, Japanese Patent Application Publication No. 2009-234781 and Japanese Patent Application Publication No. 2008-230819, creasing occurs when the recording medium is pressed with the roller.
Furthermore, in the composition disclosed in Japanese Patent Application Publication No. 11-92008, when curl occurs in the sheet, the contact surface area between the sheet and the vacuum suction wheel becomes small, and it is difficult to make a sufficiently large back tension act on the sheet.